1. Field of the Invention
This invention relates to a semiconductor light emission device (LED) such as a light emission diode, a semiconductor laser and the like.
2. Description of the Related Art
There has been remarked an AlInGaN type LED or semiconductor laser as a source of light having a wavelength shorter than 500 nm. This material has very excellent properties as a high brightness LED emitting light of a wavelength in a blue to green wavelength range (See Jpn. J. Appl. Phys. vol. 34, No. 7A, pp. L797-799 (1995): document 1) and is going to be put into practice as a light source for a signal, an outdoor display and the like. Further recently there has been reported pulse oscillation at 417 nm of a semiconductor laser at room temperatures (See Jpn. J. Appl. Phys. vol. 35, No. 1B, pp. L74-76 (1996): document 2).
The AlInGaN type semiconductor laser described in the document 2 is disadvantageous in that heat production of the device and modulation distortion are large since the operating voltage upon generation of pulse oscillation is as high as several ten volts and the power fed to the device during oscillation is not smaller than about ten times that of normal devices due to very high contact resistance between a p-type semiconductor layer and an electrode. Thus reduction of impedance of the device is a problem.
Further since the AlInGaN type semiconductor laser can produce a beam spot much smaller in diameter than that of a 630 nm semiconductor laser, which has been put into practice, can produce, application of the AlInGaN type semiconductor laser to a high density optical disk memory is expected. For this purpose, it is necessary to realize oscillation in a single mode so that a stabilized light beam is obtained, and in the case of a short wavelength range of 360 to 500 nm at which the AlInGaN type semiconductor laser is expected to oscillate, it is necessary that the width of the stripe of an optical waveguide incorporated in the device in order to stabilize the transverse mode is about 2 .mu.m or less.
However in the case of the conventional device described in the aforesaid document, since an n-type semiconductor layer is first formed on a substrate and then a p-type semiconductor layer is formed on the n-type semiconductor layer, the contact area between the p-type semiconductor layer and a p-side electrode is narrowed when a narrow stripe is formed, which further increases the impedance.
Thus there has been a demand toward reduction in the impedance of the device in a semiconductor light emission device where the resistivity of the p-type semiconductor layer is high and the contact resistance between the p-type semiconductor layer and the p-side electrode.